Doctor On Demand, a startup that lets users video chat with U.S.-certified doctors, just raised $21 million and announced its first major corporate deal.

The idea is that next time you think you might have a sinus infection, you can avoid spending an hour or two in the waiting room for a last-minute appointment, and opt instead for a hassle-free video chat with a doctor.

You pay a flat fee of $40 for each 15 minutes spent chatting with a physician, who can diagnose your issue, prescribe you simple medication, advise your next actions, or simply ease your fears.

No crowded office visit required.

Since Doctor on Demand launched in late 2013, it has signed on more than 1,400 doctors and just inked a deal with Comcast to integrate its services with the company's benefits plan.

Co-founder Adam Jackson told Business Insider that Doctor On Demand plans to use the fresh funding partially to expand its enterprise sales team. He thinks its secret sauce is that it doesn't charge companies that it partners with a per-employee per-month fee, unlike other startups in the space.

"Employers love Doctor On Demand, because it reduces sick days, and makes their employees happier and gets them better sooner," Jackson says, "Because we can give them direct access to medical care instantly."

Although 15 minutes may not sound like a long time to chat with a doctor, Jackson said that most calls only take between nine or ten minutes to resolve. He says that the most common reaction he gets from patients is, "Wow, I can't believe that actually worked."

The interesting backstory of the startup?

Jackson's co-founder, Jay McGraw, knows the medical profession from the entertainment side. He's the executive producer of TV show The Doctors and his dad is Dr. Phil.

Venrock led Doctor On Demand's $21 million round, joined by Shasta Ventures and angel investor Sir Richard Branson. The company has raised $23 million to-date.

Doctor On Demand is available for iPhone or Android.

"If you have a broken leg or you're bleeding out, don't use Doctor on Demand," Jackson says.

Before you connect with a doctor, you're asked to enter your symptoms, any allergies, and what medication you're already on.